Metal hydrates such as aluminum trihydroxide (ATH) and magnesium hydroxide (Mg(OH)2) are effective flame retardants for many polyolefin systems. However, these metal hydrates cannot be used in many systems because of shelf-life and processing issues. For example, because they absorb water from the environment, have hydroxyl groups in their structure, and partially dehydrate during processing, they give limited shelf-life and can cause scorch problems in moisture crosslinkable resins. Furthermore, polymer compounds (thermoplastic, peroxide crosslinkable, and moisture crosslinkable) containing metal hydrates must be compounded and extruded at temperatures below the dehydration temperatures of the metal hydrates in order to avoid loss of activity of these flame retardants and to avoid undesired foaming that results from dehydration of the metal hydrates. What is needed is a way to prepare polymer compounds that are flame retarded with metal hydrates yet free of the above-mentioned limitations posed by shelf-instability, extrusion scorch, undesired dehydration, and processing temperature limitations.